This is not yet solved and a very widespread issue that should not have occurred after updating the app.
From the official Adobe account via fb messenger:
"Hi, we're sorry that some of your presets and images in the Lightroom mobile app have disappeared after the recent app update. This is a known issue and our engineering team is currently investigating it. For more info on this issue, please refer and follow: https://bit.ly/31aIbVT Note: Please do not uninstall the app!” Thanks! ^NM"